System and method of refrigerating at least one enclosure

ABSTRACT

A system and method are provided for refrigerating at least one enclosure, such as an aircraft galley cart. The system includes at least one air-to-liquid heat exchanger, an eutectic thermal battery, a liquid-to-direct heat exchanger and at least one liquid-to-direct heat pump. The air-to-liquid heat exchangers are in thermal communication with the interiors of the enclosures. The thermal battery is in fluid communication with the air-to-liquid heat exchangers via a first coolant loop. The liquid-to-direct heat exchanger and the liquid-to-direct heat pumps are in fluid communication with the eutectic thermal battery via a second coolant loop, and in thermal communication with a cold heat sink, such as an aircraft fuselage skin structure. The system can controllably operate in direct passive, indirect passive, direct active and/or an indirect active modes whereby a coolant can selectively flow in the first and/or second coolant loops to thereby refrigerate the enclosures.

FIELD OF THE INVENTION

[0001] The present invention relates generally to systems and methods ofrefrigerating enclosures and, more particularly, relates to systems andmethods of refrigerating enclosures capable of integrating passive andactive cooling techniques.

BACKGROUND OF THE INVENTION

[0002] In many industries employing refrigeration systems, such as theairline, trucking, shipping and building industries, conventionalrefrigeration technology is based on the vapor-compression cycle. Inaircraft, for example, a vapor-compression cycle air chiller istypically mounted either on top of a galley of the aircraft, such as inthe crown area, or below the cabin floor, such as in the cargo areabetween floor beams. To cool consumables such as food and beverages, theair chiller is typically connected to one or more galley food storagecompartments via a series of air supply/return ducts, which collectivelyform a closed-loop system. In operation, the air chiller is essentiallya unitized air conditioner similar in principle to the conventionalwindow-unit air conditioners typically mounted in a window of a house.The objective is to maintain the temperature of the consumables between0° C. and 7° C., or between 0° C. and 5° C. (or 4° C. in many Europeancountries) as may be required in the future.

[0003] In order to maintain the consumables at a temperature within theproper temperature range, a desired temperature difference must existbetween the warmer aircraft cabin atmosphere and the cooler galley foodstorage compartments atmosphere. This temperature difference causes heatenergy in the warmer aircraft cabin to flow into the cooler galley foodstorage compartments via a combination of heat transfer mechanisms.Conventionally, the rate of this heat transfer (or heat load) at anygiven temperature differential is governed by the effective netinsulation between the warm and the cool atmospheres. In this regard,the vapor-compression cycle air chiller typically must be able to removethis heat load from the cooler food storage compartments in order tomaintain the desired temperature differential, thereby keeping theconsumables at a temperature within the proper temperature range. Theheat removed by the air chiller is rejected to the atmosphere in eitherthe airplane cargo compartment or the cabin crown, depending on thelocation of the air chiller.

[0004] Conventionally, the vapor-compression cycle air chiller is anair-to-air system. In this regard, a fan in the air chiller unitcirculates air from the galley food storage compartments via the airreturn ducts through an evaporator coil mounted inside the air chiller.Inside the evaporator coil, cold coolant, such as cold R134a refrigerant(gas phase), soaks up the heat from the air flowing across theevaporator coil. As the air flows across the evaporator coil, the airloses heat energy to the coolant. The cold air is then circulated backinto the galley food storage compartments via the air supply ducts. Onceinside the galley food storage compartments, the cold air soaks up theheat energy inside the food storage compartments. The process can thenbe repeated in a continuous manner in order to maintain the desiredtemperature differential.

[0005] As will be appreciated, once the coolant receives the heat energyfrom the air flowing across the evaporator coil, the heat energy must berejected from the coolant. In this regard, the gaseous coolant becomessuperheated as it soaks up the heat energy through the evaporator coil.The superheated gaseous coolant is then typically drawn into acompressor within the air chiller. The compressor then does work on thegaseous coolant by forcing the gaseous coolant into a smaller volume byapplying external pressure. As a result, the temperature and pressure ofthe gaseous coolant is greatly increased. The high temperature andpressure gaseous refrigerant is then circulated through a condenserlocated in the air chiller unit. As the gaseous refrigerant flowsthrough the condenser coil, a fan blows ambient air across the condensercoil to cool the hot, gaseous refrigerant. As the refrigerant circulatesthrough the condenser coil, it loses heat energy to the ambient air suchthat the refrigerant changes state from a high-pressure, super-heatedgas to a saturated high pressure liquid as it leaves the condenser coiland enters a liquid receiver. The liquid refrigerant travels through thehigh-pressure liquid line to an expansion valve (or in some systems, acapillary tube) and is expanded into a saturated gas before it re-entersthe evaporator coil.

[0006] Whereas refrigeration systems employing vapor-compression cycleair chillers are adequate for maintaining consumables at a temperaturewithin the proper temperature range, such refrigeration systems havedrawbacks. In this regard, the heart of the vapor-compression cycle airchiller is the compressor. Operation of the compressor as well as thefan blowing air across the condenser, however, undesirably consumessignificant amounts of electrical energy. Also, the compressor istypically a complicated mechanical device, which is noisy and prone tofailure. In addition, operation of the air-chiller rejects heat into thecabin environment, which can be problematic for the environmentalcontrol system (ECS) during ground operations. In this regard, ECS packsthat provide cooling to the airplane cabin and equipment during groundoperation are typically located under the airplane wing box, whichstores airplane fuel. As such, the harder the ECS system has to work inhot climates, the more heat the ECS system rejects into the airplanefuel. Rejecting heat into the airplane fuel may cause undesirable fuelvaporization in a partially full fuel tank which, in some instances, hasbeen linked to incidents of airplanes exploding on the ground due tovaporized fuel being ignited by sparks from malfunction fuel pumps.

SUMMARY OF THE INVENTION

[0007] According to embodiments of the present invention, a system andmethod are provided that are capable of refrigerating one or moreenclosures utilizing the “free” thermal potential provided by thenatural cold heat sink of a vehicle or system with which the system isoperated. Many vehicles and systems in operation today include naturalcold heat sinks capable of absorbing heat from various sources. In theaircraft industry, for example, during normal cruising flight at highaltitude, the ambient atmosphere temperature outside the aircraft canrange from −40° F. to approximately −80° F. As a result, the skinstructure of the aircraft, such as the fuselage skin structure, canreach temperatures far below the internal aircraft cabin temperature,which is generally maintained at approximately +70° F.

[0008] The system and method of embodiments of the present invention arebased on a hybrid refrigeration methodology capable of integratingpassive and active cooling technologies to provide continuousrefrigeration to enclosures, such as aircraft galley carts.Advantageously, the systems and methods of embodiments of the presentinvention are capable of achieving an optimal balance between therefrigeration capability of the system and the changing operationalenvironment of the cold heat sink. As such, the system and method canrefrigerate enclosures, such as galley carts on aircraft, without theuse of a vapor-compression-cycle air chiller, thereby avoiding thedrawbacks of vapor-compression-cycle air chillers.

[0009] According to one aspect of the present invention, a system isprovided for refrigerating at least one enclosure, such as an aircraftgalley cart. The system includes at least one air-to-liquid heatexchanger in thermal communication with the interiors of the enclosures.The system also includes an eutectic thermal battery (a cold storagedevice) in fluid communication with the air-to-liquid heat exchangersvia a first coolant loop. In turn, the system includes aliquid-to-direct heat exchanger in fluid communication with the eutecticthermal battery via a second coolant loop. Advantageously, theliquid-to-direct heat exchanger is also in thermal communication with acold heat sink, such as an aircraft fuselage skin structure. Also inthermal communication with the cold heat sink and fluid communicationwith the eutectic thermal battery, the system includes at least oneliquid-to-direct heat pump.

[0010] The system is capable of controllably operating in a directpassive mode, an indirect passive mode, a direct active mode and/or anindirect active mode whereby a coolant is capable of selectively flowingin the first and/or second coolant loops through the air-to-liquid heatexchangers, the eutectic thermal battery, the liquid-to-direct heatexchanger and/or the liquid-to-direct heat pumps. In this regard, thesystem can additionally include a plurality of valves capable ofcontrolling the flow of coolant in the first and second coolant loops.Further, the system can include first and second coolant pumps that arecapable of driving the coolant in the first and second coolant loops,respectively.

[0011] When the system operates in the indirect passive mode, theair-to-liquid heat exchangers are capable of placing the coolant in thefirst coolant loop in thermal communication with interiors such that thecoolant can carry heat away from the interiors. The eutectic thermalbattery can then receive the coolant from the air-to-liquid heatexchangers, and then absorb the heat carried away by the coolant, suchas via a phase change material in the eutectic thermal battery. Theliquid-to-direct heat exchanger can thereafter receive the coolant inthe second coolant loop such that the cold heat sink can absorb the heatcarried by the coolant.

[0012] In operation in direct passive mode, the air-to-liquid heatexchangers are capable of placing the coolant in the first coolant loopin thermal communication with interiors such that the coolant can carryheat away from the interiors. The coolant in the first coolant loop canthen be received by the second coolant loop, and thereafter be receivedby the liquid-to-direct heat exchanger. The liquid-to-direct heatexchanger can thereafter receive the coolant in the second coolant loopsuch that the cold heat sink can absorb the heat carried by the coolant.

[0013] When the system operates in the direct active mode, theair-to-liquid heat exchangers are capable of placing the coolant in thefirst coolant loop in thermal communication with the interiors of theenclosures such that the coolant can carry heat away from the interiors.The liquid-to-direct heat pumps can then reject the heat carried by thecoolant in the first coolant loop to the cold heat sink. In analternative embodiment, the system further includes (or have access to)a store of a pressurized inert composition, such as Nitrogen. In thisembodiment, the eutectic thermal battery includes an evaporator coil invariable fluid contact with the store. Also in this embodiment, when thesystem operates in the direct active mode the eutectic thermal batteryis capable of receiving the coolant from the air-to-liquid heatexchangers, and thereafter absorbing the heat carried away by thecoolant in the first coolant loop. The pressurized inert composition canthen be expanded into the evaporator coil, such as a low temperaturevapor, to thereby carry away the heat absorbed by the eutectic thermalbattery. After the pressurized inert composition absorbs heat from thephase change material within the eutectic thermal battery, the inertcomposition can exit the eutectic thermal battery, such as through avapor line that can eject the inert composition from the airplane.

[0014] When the system operates in the indirect active mode, coolant inthe second coolant loop is capable of being placed in thermalcommunication with the eutectic thermal battery such that the coolantcarries heat away from the eutectic thermal battery. Theliquid-to-direct heat pumps can then be capable of rejecting the heatcarried by coolant in the second coolant loop.

[0015] In various embodiments, the first and/or second coolant loops areclosed loops. Therefore, for example, when the first coolant loop is aclosed loop and the system is operating in the indirect passive mode,the air-to-liquid heat exchangers are capable of receiving the coolantfrom the eutectic thermal battery after the heat has been absorbed fromthe coolant. Similarly, when the second coolant loop is a closed loopand the system is operating in the indirect passive mode, the eutecticthermal battery is capable of receiving the coolant from theliquid-to-direct heat exchanger after the cold heat sink absorbs theheat carried away by the coolant. When the second coolant loop is aclosed loop and the system is operating in the indirect active mode, forexample, the eutectic thermal battery is capable of receiving thecoolant from the liquid-to-direct heat pumps after the liquid-to-directheat pumps reject the heat carried by the coolant to the cold heat sink.

[0016] A method of refrigerating at least one enclosure is alsoprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Having thus described the invention in general terms, referencewill now be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

[0018]FIG. 1 is a schematic block diagram of a system for refrigeratingat least one enclosure according to one embodiment of the presentinvention;

[0019]FIG. 2 illustrates various elements of a system for refrigeratingat least one enclosure according to one embodiment of the presentinvention, where the system is utilized in an aircraft having a coldheat sink comprising at least a portion of the aircraft fuselage skinstructure;

[0020]FIG. 3 is a schematic block diagram of a system for refrigeratingat least one enclosure in a direct passive mode according to oneembodiment of the present invention;

[0021]FIG. 4 is a schematic block diagram of a system for refrigeratingat least one enclosure in an indirect passive mode according to oneembodiment of the present invention;

[0022]FIG. 5 is a schematic block diagram of a system for refrigeratingat least one enclosure in a direct active mode according to oneembodiment of the present invention;

[0023]FIG. 6 is a schematic block diagram of a system for refrigeratingat least one enclosure according to another embodiment of the presentinvention;

[0024]FIG. 7 is a schematic block diagram of a system for refrigeratingat least one enclosure in a direct active mode according to anotherembodiment of the present invention;

[0025]FIG. 8 is a schematic block diagram of a system for refrigeratingat least one enclosure in an indirect active mode according to oneembodiment of the present invention; and

[0026]FIG. 9 is a schematic block diagram of a system for refrigeratingat least one enclosure in a direct active mode according to yet anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

[0028] Embodiments of the present invention provide a system and methodof refrigerating at least one enclosure. As described herein, the systemand method are utilized within an aircraft to refrigerate one or moregalley food storage compartments. The system and method are thereforeparticularly advantageous for cooling consumables, such as food andbeverages, in an aircraft. It should be appreciated, however, that thesystem and method can be utilized in other vehicles or with othersystems, without departing from the spirit and scope of the presentinvention. In this regard, the system and method can be utilized in anyof a number of other vehicles or with other systems capable of providinga cold heat sink in a manner similar to that described below.

[0029] Advantageously, embodiments of the present invention are capableof operating in a number of different modes to provide the most costeffective and efficient refrigeration of the enclosure(s). In thisregard, embodiments of the present invention are capable of operatingwith an already existing cold heat sink in the vehicle or other systemwithin which the invention is utilized to provide passive refrigerationof the enclosure(s). As utilized in aircraft, for example, the system iscapable of operating with the aircraft fuselage skin structure acting asthe cold heat sink.

[0030] Typically, the temperature of a fuselage skin structure of anaircraft during normal high altitude cruising is between approximately−40° F. and −80° F. Such a super cold skin temperature enables thefuselage skin to function as a powerful cold heat sink. Thus, when thefuselage skin has a temperature low enough to act as a cold heat sink,such as during flight, embodiments of the present invention canpassively refrigerate the enclosures by utilizing the fuselage skin.When the fuselage skin does not have a temperature low enough to providean effective heat sink, such as while an aircraft is on the ground,embodiments of the present invention are capable of actively and/orpassively refrigerating the enclosures. Embodiments of the presentinvention can therefore provide continuous refrigeration of theenclosures until such time as the temperature of the fuselage skindecreases to a point that the fuselage skin can act as an effective heatsink.

[0031] Reference is now made to FIG. 1, which illustrates a system 10for refrigerating at least one enclosure 11 according to one embodimentof the present invention where the system operates within an aircraft,and where the enclosures comprise galley food storage compartments. Itshould be appreciated, however, that even operating the system within anaircraft, the enclosures can comprise any of a number of otherenclosures without departing from the spirit and scope of the invention.As shown, the system includes an eutectic thermal battery 12, aliquid-to-direct heat exchanger 14, at least one liquid-to-direct heatpump 16 and at least one air-to-liquid heat exchanger 18. In addition,the system includes a plurality of valves, such as valves V1, V2, V3,V4, V5 and V6, as well as coolant pumps 20 and 22, that allow coolant topass through various of the other elements of the system during variousmodes of operation, as described below. Although not shown for clarity,it will be appreciated by those skilled in the art that the coolantpumps will typically also include coolant reservoirs for properoperation of the coolant pumps. To allow coolant to pass through variousof the other elements, the valves are connected to coolant ducts 13,pipes or the like that interconnect the elements of the system. Thecoolant can comprise any of a number of different coolants such as, forexample, TYFOXIT F brand coolant manufactured by Tyforop Chemie GmbH ofHamburg, Germany.

[0032] The eutectic thermal battery 12 functions within the system 10 asa thermal energy capacitor. More particularly, in one embodiment, theeutectic thermal battery comprises a highly-insulated, two-passcold-holding plate that contains a phase change material that has apredetermined freezing point. The phase change material can comprise anyof a number of different materials having any of a number of differentfreezing points, such as between 0° C. and −40° C. As indicated above inthe context of aircraft, the super cold temperature of the fuselage skinenables the fuselage skin to function as a powerful cold heat sink. Assuch, the fuselage skin structure can be utilized to rapidly absorblatent heat from the phase change material inside the eutectic thermalbattery, as described below. When the phase change material looses itslatent heat to the cold heat sink, it changes phase from a liquid to asolid-liquid mixture and eventually to a pure solid once all the latentheat is given up. Typically, the latent heat transfer takes placeisothermally at a temperature between 0° C. and −40° C. Therefore, thephase change material can be selected as desired to have a freezingtemperature capable of refrigerating the enclosures to within a desiredtemperature range. In one embodiment, for example, the phase changematerial comprises PlusICE E-12 phase change material manufactured byEnvironmental Process Systems Limited of the United Kingdom. The PlusICEE-12 phase change material has a freezing point of −1.6° C.

[0033] The system includes a series of ducts 13 arranged in one of twoclosed-loop paths (designated L1 and L2) through which coolant flowsbetween and through various of the system elements. More particularly,the eutectic thermal battery 12 contains two separate internal coolantloops. One of the coolant loops provides heat transfer between theeutectic thermal battery and the air-to-liquid heat exchangers 18 vialoop L1. The air-to-liquid heat exchangers act to carry heat out of theenclosures 11. In this regard, the air-to-liquid heat exchangers aredisposed in thermal contact with the interior of the enclosures, such asby being mounted within the enclosures. The system can include anynumber of air-to-liquid heat exchangers and, in one embodiment, thesystem includes one air-to-liquid heat exchanger in each enclosure to berefrigerated. The air-to-liquid heat exchangers can comprise any of anumber of different devices known to those skilled in the art. Forexample, the air-to-liquid heat exchangers can comprise any of a numberof air-to-liquid heat exchangers manufactured by Lytron of Woburn, Mass.

[0034] In addition to the coolant loop providing heat transfer betweenthe eutectic thermal battery 12 and the air-to-liquid heat exchangers18, the eutectic thermal battery includes a second internal loop L2. Thesecond internal coolant loop provides heat transfer between the eutecticthermal battery and the liquid-to-direct heat exchanger 14, or betweenthe eutectic thermal battery and the liquid-to-direct heat pumps 16. Theliquid-to-direct heat exchanger and the liquid-to-direct heat pumps canbe located in any number of different locations in thermal contact witha cold heat sink, typically a cold heat sink of a vehicle or othersystem employing the system 10. In this regard, the liquid-to-directheat exchanger and the liquid-to-direct heat pumps can be disposed inthermal contact with the cold heat sink in any of a number of differentmanners.

[0035] In one embodiment, for example, the liquid-to-direct heatexchanger 14 and the liquid-to-direct heat pumps 16 are disposed inthermal contact with the cold heat sink by placing the liquid-to-directheat exchanger and the liquid-to-direct heat pumps in physical contactwith the cold heat sink. In embodiments where the system is utilized inan aircraft, for example, the liquid-to-direct heat exchanger and theliquid-to-direct heat pumps can be mounted in physical, and thusthermal, contact with the aircraft fuselage skin structure. In thisregard, reference is made to FIG. 2, which illustrates fourliquid-to-direct heat exchangers 14 mounted in physical contact with aportion of an aircraft fuselage skin structure 32, such as in thelocation of the forward galley complex of the aircraft.

[0036] The liquid-to-direct heat exchanger 14 is sized to have thecooling capacity required to accommodate the total heat load from all ofthe air-to-liquid heat exchangers 18, as well as the capacity to removethe required latent heat to freeze the phase change material in theeutectic thermal battery 12 within a desirable time period when the coldheat sink is capable of passively absorbing the heat from the coolant,such as during high altitude flight. As will be appreciated, however,the system 10 can include multiple liquid-to-direct heat exchangers thatcollectively have the required cooling capacity. The liquid-to-directheat exchanger can comprise any of a number of different devices as suchare known to those skilled in the art such as, for example, any of anumber of cold plates manufactured by Lytron. In one advantageousembodiment, the shape of the liquid-to-direct heat exchanger ispreferably designed to fit the contour of the cold heat sink (e.g.,fuselage skin structure), as shown in FIG. 2. By fitting the shape ofthe liquid-to-direct heat exchanger to the contour of the cold heatsink, the liquid-to-direct heat exchanger can be in better thermalcontact with the cold heat sink.

[0037] Like the liquid-to-direct heat exchanger 14, the liquid-to-directheat pumps 16 are sized to have the collective cooling capacity requiredto accommodate the total heat load from all of the air-to-liquid heatexchangers 18. In this regard, the system 10 can include any number ofliquid-to-direct heat pumps. As will be appreciated, however, the systemcan include a single liquid-to-direct heat pump that has the requiredcooling capacity. The liquid-to-direct heat pumps can comprise any of anumber of different devices as such are known to those skilled in theart. In this regard, the liquid-to-direct heat pumps can comprise any ofa number of different thermoelectric or thermionic liquid-to-direct heatpumps, as such are known to those skilled in the art. For example, theliquid-to-direct heat pumps can comprise any of a number of differentliquid-to-direct heat pumps manufactured by Supercool AB of Goteborg,Sweden. Also like the liquid-to-direct heat exchanger, the shape of theliquid-to-direct heat pumps in one advantageous embodiment are designedto fit the contour of the cold heat sink (e.g., fuselage skin structure)such that the liquid-to-direct heat pumps can be in better thermalcontact with the cold heat sink.

[0038] As indicated above, the system 10 is capable of operating in anumber of different modes to provide continuous refrigeration to theenclosures 11. Typically, the system is capable of operating in one offour modes, direct passive, indirect passive, direct active or indirectactive. Depending on the mode of operation, coolant flows throughout thesystem in various manners while being driven by the coolant pumps 20 and22, which can comprise variable or constant-speed coolant pumps. Tocontrol the mode of operation, and thus the flow path of the coolant,the valves V1-V6 are open and shut in various combinations. In oneembodiment, then, the valves can comprise remote-controlled shut-offvalves. As will be appreciated, the mode of operation can be selected inany of a number of different manners. For example, the mode of operationcan be selected at least partially based upon the temperatures of thephase change material and/or the coolant, as well as the temperatures ofthe cold heat sink, the coils within the air-to-liquid heat exchangers18 and/or the interiors of the enclosures 11. In addition, the mode ofoperation can be selected based upon the refrigeration needs of theenclosures, as the enclosures may not require refrigeration in someinstances.

[0039] To control the mode of operation, the system 10 can additionallyinclude a controller (not shown) electrically connected to the valvesV1-V6. In addition, the controller can be electrically connected totemperature sensors (also not shown), which can be mounted in thermalcontact with the phase change material, the coolant, the cold heat sink,the coils within the air-to-liquid heat exchangers 18 and/or theinteriors of the enclosures 11. Based on temperature informationtransmitted to the controller from one or more temperature sensors,then, the controller can determine a mode of operation for the system tooperate. Thereafter, the controller can operate the valves, as describedbelow, to operate the system in the respective modes. As will beappreciated, as the mode of operation can change, the controller can beadapted to continuously receive temperature information, oralternatively receive temperature information at a predetermined timeinterval.

[0040] To operate the system 10 in direct passive mode, valves V1, V3,V6 are opened to permit coolant to pass through the ducts 13A and 13Bconnected to the respective valves; and valves V2, V4, V5 are closed toprevent coolant from passing through the ducts connected to therespective valves. With reference to FIG. 3 illustrating an operationalblock diagram of the system operating in direct passive mode. Inoperation in direct passive mode, powered by the coolant pumps 20 and22, coolant passes through loops L1 and L2. As the coolant passesthrough loop L1, coolant having a temperature less than the internaltemperature of the enclosures 11 passes through the air-to-liquid heatexchangers 18, which are in thermal contact with the interiors ofrespective enclosures.

[0041] As the coolant passes through the air-to-liquid heat exchangers18, the coolant absorbs heat from the interiors of the respectiveenclosures 11, and thereafter carries the heat away from the enclosures.As the heat is carried away from the interiors, the temperature in theinteriors drops, thereby refrigerating the interiors to within apredetermined temperature range. Thereafter, to reject the absorbedheat, the coolant is passed through the ducts 13B to the ducts 13A tothe liquid-to-direct heat exchanger 14, which is in thermal contact withthe cold heat sink. The coolant then passes through the liquid-to-directheat exchanger, where the heat is absorbed by the cold heat sink.

[0042] Operating the system 10 in direct passive mode advantageouslyallows the system to utilize an existing, typically passive, cold heatsink (e.g., fuselage skin) of a vehicle (e.g., aircraft) or other systememploying the system. In this regard, the system is capable of operatingin the direct passive mode as long as the coolant is capable ofmaintaining a low enough thermodynamic state to facilitate adequate heattransfer out of the enclosures 11. More particularly, the system canadvantageously operate in the direct passive mode when the cold heatsink is at a temperature between the temperature of phase changematerial in the eutectic thermal battery 12 and approximately 0° C.

[0043] To operate the system 10 in indirect passive mode, valves V1, V4and V5 are opened to permit coolant to pass through the ducts 13A and13B connected to the respective valves; and valves V2, V3 and V6 areclosed to prevent coolant from passing through the ducts connected tothe respective valves. In this regard, reference is now made to FIG. 4,which illustrates an operational block diagram of the system operatingin indirect passive mode. In operation in indirect passive mode, poweredby the coolant pump 22, coolant passes through loop L1. As the coolantpasses through loop L1, coolant having a temperature less than theinternal temperature of the enclosures 11 passes through theair-to-liquid heat exchangers 18, which are in thermal contact with theinteriors of respective enclosures.

[0044] As the coolant passes through the air-to-liquid heat exchangers18, the coolant absorbs heat from the interiors of the respectiveenclosures 11, and thereafter carries the heat away from the enclosures.As the heat is carried away from the interiors, the temperature in theinteriors drops, thereby refrigerating the interiors to within apredetermined temperature range. Thereafter, to reject the absorbedheat, the coolant is passed through the ducts 13B to the eutecticthermal battery 12 where the coolant then passes through the eutecticthermal battery. In this regard, as the coolant passes through theeutectic thermal battery, the phase change material in the eutecticthermal battery absorbs the heat from the coolant, thereby decreasingthe temperature of the coolant. With the coolant loop L1 typicallycomprising a closed loop, the process can then repeat, beginning withthe coolant passing back through the air-to-liquid heat exchangers.

[0045] When the cold heat sink (e.g., aircraft fuselage skin structure)temperature is lower than the phase change material, circulation ofcoolant in loop L2 is enabled to remove the heat from the phase changematerial. Powered by coolant pump 20, coolant passing through theeutectic thermal battery 12 in loop L2 absorbs the heat in the phasechange material. Thereafter, the coolant passes through the ducts 13A tothe liquid-to-direct heat exchanger 14, which is in thermal contact withthe cold heat sink. The coolant then passes through the liquid-to-directheat exchanger, where the heat is absorbed by the cold heat sink.

[0046] By removing the heat from the phase change material, the phasechange material in the eutectic thermal battery 12 can be maintained aseither a liquid-solid mixture or a slightly sub-freezing solid as thephase change material absorbs heat from the coolant flowing in loop L1and rejects the heat to the cold heat sink via coolant flowing throughloop L2. In this regard, the system 10 can manage the phase changematerial phase mixture by controlling the coolant flow rates throughloops L1 and L2 as the coolant passes through the eutectic thermalbattery, as will be appreciated by those skilled in the art. Theobjective, then, is to maintain isothermal heat transfer between thecoolant in loop L1 and the phase change material, and the phase changematerial and the coolant in loop L2. Advantageously, by maintainingisothermal heat transfer in the eutectic thermal battery, the system canrefrigerate the interior of the enclosures without causing theconsumables in the enclosures to freeze.

[0047] In some instances, such as when the enclosures 11 do not containany consumables and maintenace of the temperature within the enclosuresis not needed, the system 10 can allow the phase change material in theeutectic thermal battery 12 to reach a sub-freezing solid state, whichcan provide extra refrigeration capacity for ground operation duringairport turnaround service. To allow the phase change material to reacha sub-freezing solid state, the valves can be operated to permitcontinuous flow of coolant through coolant loop L2 until the phasechange material in the euctectic thermal battery 12 reaches the desiredtemperature.

[0048] Operating the system 10 in indirect passive mode advantageouslyallows the system to utilize an existing, typically passive, cold heatsink (e.g., fuselage skin) of a vehicle (e.g., aircraft) or other systememploying the system. In this regard, the system is capable of operatingin the indirect passive mode as long as the phase change material in theeutectic thermal battery 12 is capable of maintaining a low enoughthermodynamic state to facilitate adequate heat transfer out of theenclosures 11. As will be appreciated, however, the thermodynamic stateof the phase change material in some instances is too high to enable thesystem to operate in the indirect passive mode. For example, ininstances where the vehicle comprises an aircraft and the cold heat sinkcomprises the aircraft fuselage skin, such an occasion might berepresentative of an instance where the aircraft is scheduled forrevenue service after maintenance. Additionally, for example, abnormallylong delays in airport turnaround service can also potentially exhaustthe refrigeration capacity of the eutectic thermal battery 12. In suchinstances, the system is advantageously capable of operating in a directactive mode and/or an indirect active mode to provide continuousrefrigeration to the enclosures, as such may be determined by theaforementioned controller.

[0049] In either direct or indirect active mode, the system 10 iscapable of utilizing the liquid-to-direct heat pumps 16. As indicatedabove, the liquid-to-direct heat pumps can be located in any number ofdifferent locations in thermal contact with the cold heat sink (e.g.,fuselage skin structure). To utilize the liquid-to-direct heat pumps,then, the liquid-to-direct heat pumps are connected to the eutecticthermal battery 12 via a series of ducts 13 within coolant loop L2, andconnected to the air-to-liquid heat exchangers 18 in the enclosures 11via a series of ducts within coolant loops L1 and L2.

[0050] In direct active operation, coolant is circulated between theliquid-to-direct heat pumps 16 and the air-to-liquid heat exchangers 18in the enclosures 11 via coolant loops L1 and L2. Thus, to operate thesystem in direct active mode, valves V2, V3 and V6 are opened to permitcoolant to pass through the ducts 13 connected to the respective valves;and valves V1, V4 and V5 are closed to prevent coolant from passingthrough the ducts connected to the respective valves. Reference is nowmade to FIG. 5, which illustrates an operational block diagram of thesystem operating in direct active mode.

[0051] During operation of the system 10 in direct active mode, directcoolant circulation is enabled between the air-to-liquid heat exchangers18 and the liquid-to-direct heat pumps 16. Powered by one or bothcoolant pump 20 and coolant pump 22, coolant is passed through theair-to-liquid heat exchangers, which are in thermal contact with theinteriors of the respective enclosures 11. Like during indirect passivemode operation, when the coolant passes through the air-to-liquid heatexchangers, the coolant absorbs heat from the interiors of therespective enclosures, and thereafter carries the heat away from theenclosures. As the heat is carried away from the interiors of theenclosures, the temperature in the interiors drops, therebyrefrigerating the interiors to a predetermined temperature.

[0052] To reject the heat absorbed by the coolant in the direct activemode, the coolant is passed through portions of ducts 13A and 13B to theliquid-to-direct heat pumps 16. The coolant then passes through theliquid-to-direct heat pumps, which are in thermal contact with the coldheat sink (e.g., aircraft fuselage skin structure). As the coolantpasses through the liquid-to-direct heat pumps, the heat is rejected tothe cold heat sink. As will be appreciated, in instances in which thesystem 10 operates in active mode (either direct or indirect), thetemperature of the cold heat sink may not be sufficiently low topassively absorb heat from the coolant. As such, the liquid-to-directheat pumps are capable of forcing the transfer of heat from the coolantto the cold heat sink, as such is well known to those skilled in theart. After the heat in the coolant is rejected to the cold heat sink,the process can be repeated, beginning with the coolant passing backthrough the air-to-liquid heat exchangers 18.

[0053] In an alternative embodiment shown in FIG. 6, the system 10 caninclude or othwerwise access a store 24 of a compressed inertcomposition, such as compressed nitrogen, nitrogen-enriched air, carbondioxide or the like. In this regard, the system can operate in directactive mode by expanding the compressed inert composition to ambientatomspheric pressure. To utilize the store of inert composition, theeuctectic thermal battery 12 can include an evaporator coil 26, which isin variable fluid contact with the store, such as via a throttling valve28. To operate the system 10 in direct active mode in this alternativeembodiment, then, valve V5 is opened to permit coolant to pass throughthe ducts 13 connected to the respective valves; and valves V1, V2, V3,V4 and V6 are closed to prevent coolant from passing through the ductsconnected to the respective valves. Also, during operation of the systemin this embodiment, the throttling valve is controllably opened andclosed, as described below. In this regard, reference is now made toFIG. 7, which illustrates an operational block diagram of the systemoperating in direct active mode in embodiments including the store ofinert composition.

[0054] In direct active operation according to the embodiment of FIGS. 5and 6, powered by the coolant pump 22, coolant passes through loop LI ina manner similar to that during operation of the system 10 in indirectpassive mode. In this regard, coolant having a temperature less than theinternal temperature of the enclosures 11 passes through theair-to-liquid heat exchangers 18 where the coolant absorbs heat from theinteriors of the respective enclosures, and thereafter carries the heataway. As the heat is carried away from the interiors, the temperature inthe interiors drops, thereby refrigerating the interiors to within apredetermined temperature range. Thereafter, to reject the absorbedheat, the coolant is passed through the ducts to the eutectic thermalbattery 12 where the phase change material in the eutectic thermalbattery absorbs the heat from the coolant, thereby decreasing thetemperature of the coolant. The process can then repeat, beginning withthe coolant passing back through the air-to-liquid heat exchangers 18.

[0055] To reject the absorbed heat from the phase change material, theinert composition can be expanded through the throttling valve 28 intothe evaporator coil 26 inside the eutectic thermal battery 12. Thesuper-cold composition can then act as a very powerful refrigerant tocool the phase change material. In this regard, the phase changematerial in the eutectic thermal battery typically gradually freezes asthe latent heat of fusion of the phase change material is lost to thecold nitrogen vapor through the walls of the evaporator coil. Theeutectic thermal battery can then provide adequate refrigeration to theenclosures, with the temperature of the phase change material typicallymaintained at or slightly below the freezing point of the phase changematerial. After cooling the phase change material, the spent compositioncan be ejected out of the aircraft, such as via an air hose connectingthe evaporator coil to a purge valve mounted to the aircraft skinstructure.

[0056] Advantageously, as used in vehicles such as aircraft, the system10 need not include the store of inert composition. In such instances,the system may utilize a store of inert composition existing onboard theaircraft for other purposes, such as preventing fuel tank explosion. Asis well known to those skilled in the art, liquid nitrogen hashistorically been used on aircraft for galley refrigeration. Such apractice has decreased in recent years due to the expanse of carryingliquid nitrogen tanks onboard aircraft. A recent Federal AviationAdministration (FAA) requirement to prevent fuel tank explosion,however, may necessitate that aircraft provide means to inert theatmosphere inside the aircraft fuel tanks. In this regard, nitrogen gasor nitrogen-enriched air are considered by many as the leadingcandidates to be used as the innerting agent inside aircraft fuel tanks.As such, future aircraft may be required to have either ground-based oraircraft-based nitrogen storage or generation capability, which thesystem can utilize to absorb heat from the phase change material.

[0057] Again referring to FIG. 1 as indicated above, in addition tooperating in the passive or direct active modes, the system 10 canoperate in an indirect active mode. In this regard, active mode can betriggered in situations, for example, when passive refrigeration is notpossible due to the temperature of the cold heat sink and currentrefrigeration of the enclosures 11 is not necessary, but cooling thephase change material is desired to “store” thermal energy forsubsequent refrigeration of the enclosures. To operate the system inindirect active mode according to one embodiment, valves V2 and V4 areopened to permit coolant to pass through the ducts 13 connected to therespective valves; and valves V1, V3, V5 and V6 are closed to preventcoolant from passing through the ducts connected to the respectivevalves. Reference is now made to FIG. 8, which illustrates anoperational block diagram of the system operating in indirect activemode. As seen then, during operation of the system in indirect activemode, coolant circulation bypasses the liquid-to-direct heat exchanger14 and the air-to-liquid heat exchangers 18 in thermal contact with theinteriors of respective enclosures 11.

[0058] During operation in indirect active mode, like during operationin indirect passive mode, coolant is passed through the eutectic thermalbattery 12 to absorb the heat in the phase change material. Thereafter,the coolant passes through the ducts 13 and through the liquid-to-directheat pumps 16, which are in thermal contact with the cold heat sink(e.g., aircraft fuselage skin structure). As the coolant passes throughthe liquid-to-direct heat pumps, the liquid-to-direct heat pumps rejectthe heat in the coolant to the cold heat sink. After the heat in thecoolant is rejected to the cold heat sink, the process can be repeated,beginning with the coolant passing back through the eutectic thermalbattery. By operating the system 10 in the indirect active mode, thephase change material in the eutectic thermal battery can be cooled,typically to the point of freezing, such that the system can thereafteroperate in the indirect passive mode to refrigerate the interiors of theenclosures.

[0059] As described above according to various embodiments of thepresent invention, the system 10 can controllably operate in either adirect passive mode, an indirect passive mode, direct active mode (withor without utilizing an inert composition) or an indirect active mode.For a summary of the state of the various valves of the system (i.e.,V1-V6) during operation of the system in the different modes, see Table1 below. TABLE 1 Direct Indirect Direct Direct Active Indirect PassivePassive Active Mode (Inert Active Valve Mode Mode Mode Gas) Mode V1 OpenOpen Closed Closed Closed V2 Closed Closed Open Closed Open V3 OpenClosed Open Closed Closed V4 Closed Open Closed Closed Open V5 ClosedOpen Closed Open Closed V6 Open Closed Open Closed Closed

[0060] It should be noted that although the foregoing may have describedthe modes of operation of the system 10 as depending on separateinstances, the system can operate in any mode at any instance, subjectonly to the thermodynamic state (or temperature) of the cold heat sink.For example, the system can operate in either the direct active orindirect active modes at instances in which the system can equallyoperate in the indirect passive mode.

[0061] It should also be understood that whereas the system may includethe various elements as described herein, the system may additionally oralternatively incorporate other valves, reservoirs, demineralizers,accumulators, heat exchangers, heat pumps, sensors, other flow loopcontrol and instrumentation devices or the like as may be required bythe system to maintain temperature, flow rate, and pressure of thecoolant and/or phase change material within prescribed limits. Forexample, the system 10 can comprise the elements as shown in FIG. 6, butnot include the liquid-to-direct heat pumps 16 or valve V2, as shown inFIG. 9. In place of the liquid-to-direct heat pumps, then, the systemcould include an air-to-liquid heat pump 19 in thermal contact with eachenclosure 11, along with additional valves V7 and V8 controlling theflow of coolant to the air-to-liquid heat exchangers 18 andair-to-liquid heat pumps. In an indirect active mode, valve V7 can beclosed and valve V8 opened to control the flow of coolant through theair-to-liquid heat pumps. As such, the air-to-liquid heat pumps canforce the transfer of heat from the interior of the enclosures to thecoolant, which can thereafter be absorbed by the cold heat sink via theliquid-to-direct heat exchanger 14.

[0062] Therefore, the system and method of the present invention arecapable of refrigerating one or more enclosures utilizing the “free”thermal potential provided by the natural cold heat sink of a vehicle orsystem with which the system is operated. Advantageously, when thesystem and method are operated onboard an aircraft, for example, thesystem and method can refrigerate enclosures, such as galley carts onaircraft, without the use of a vapor-compression-cycle air chiller,thereby avoiding the drawbacks of the vapor-compression-cycle airchiller. The system and method of embodiments of the present inventionare based on a hybrid refrigeration methodology capable of integratingpassive and active cooling technologies to provide continuousrefrigeration to enclosures, such as aircraft galley carts.

[0063] Many modifications and other embodiments of the invention willcome to mind to one skilled in the art to which this invention pertainshaving the benefit of the teachings presented in the foregoingdescriptions and the associated drawings. Therefore, it is to beunderstood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A system for refrigerating at least one enclosurecomprising: at least one air-to-liquid heat exchanger capable of placinga coolant in a first coolant loop in thermal communication with at leastone interior of the at least one enclosure such that the coolant cancarry heat away from the at least one interior; and an eutectic thermalbattery including a phase change material, wherein the eutectic thermalbattery is capable of receiving the coolant from the at least oneair-to-liquid heat exchanger and thereafter placing the coolant inthermal communication with the phase change material such that the phasechange material can absorb the heat carried away by the coolant in thefirst coolant loop.
 2. A system according to claim 1 further comprisinga first pump capable of driving the coolant in the first coolant loop.3. A system according to claim 1, wherein the first coolant loop is aclosed loop such that the at least one air-to-liquid heat exchanger iscapable of receiving the coolant from the eutectic thermal battery afterthe phase change material absorbs the heat carried away by the coolant.4. A system according to claim 1, wherein the heat absorbed by the phasechange material is capable of being carried away by a coolant in asecond coolant loop, and wherein the system further comprises aliquid-to-direct heat exchanger capable of receiving the coolant in thesecond coolant loop such that a cold heat sink in thermal communicationwith the liquid-to-direct heat exchanger can absorb the heat carried bythe coolant.
 5. A system according to claim 4 further comprising asecond pump capable of driving the coolant in the second coolant loop.6. A system according to claim 4, wherein the second coolant loop is aclosed loop such that the eutectic thermal battery is capable ofreceiving the coolant from the liquid-to-direct heat exchanger after thecold heat sink absorbs the heat carried away by the coolant.
 7. A systemaccording to claim 4, wherein the cold heat sink comprises at least aportion of an aircraft fuselage skin structure, and wherein theliquid-to-direct heat exchanger is shaped based upon a contour of atleast a portion of the fuselage skin structure.
 8. A system according toclaim 1 further comprising a store of a pressurized inert composition,wherein the eutectic thermal battery includes an evaporator coil inthermal contact with the phase change material and in variable fluidcontact with the store, wherein the pressurized inert composition iscapable of being expanded into the evaporator coil such that the inertcomposition is capable of carrying away the heat absorbed by the phasechange material.
 9. A system for refrigerating at least one enclosurecomprising: at least one air-to-liquid heat exchanger capable of placinga coolant in a coolant loop in thermal communication with at least oneinterior of the at least one enclosure such that the coolant can carryheat away from the at least one interior; and at least oneliquid-to-direct heat pump capable of rejecting the heat carried by thecoolant in the coolant loop; and a cold heat sink in thermalcommunication with the at least one liquid-to-direct heat pump, whereinthe cold heat sink is capable of receiving the heat rejected by the atleast one liquid-to-direct heat pump, and wherein the cold heat sinkcomprises at least a portion of an aircraft fuselage skin structure. 10.A system according to claim 9 further comprising: at least one pumpcapable of driving the coolant in the coolant loop.
 11. A systemaccording to claim 9, wherein the coolant loop is a closed loop suchthat the at least one air-to-liquid heat exchanger is capable ofreceiving the coolant from the at least one liquid-to-direct heat pumpafter the at least one liquid-to-direct heat pump rejects the heat tothe cold heat sink.
 12. A system for refrigerating at least oneenclosure comprising: an eutectic thermal battery including a phasechange material, wherein the phase change material is capable ofabsorbing heat carried away from at least one interior of the at leastone enclosure, and wherein the eutectic thermal battery is capable ofreceiving a coolant from a second coolant loop and thereafter placingthe coolant in thermal communication with the phase change material suchthat the coolant can absorb heat from the phase change material; and atleast one liquid-to-direct heat pump capable of rejecting the heatcarried by the coolant in the second coolant loop to a cold heat sink inthermal communication with the at least one liquid-to-direct heat pump.13. A system according to claim 12 further comprising a second pumpcapable of driving the coolant in the second coolant loop from theeutectic thermal battery to the at least one liquid-to-direct heat pump.14. A system according to claim 12, wherein the second coolant loop is aclosed loop such that the eutectic thermal battery is capable ofreceiving the coolant from the at least one liquid-to-direct heat pumpafter the at least one liquid-to-direct heat pump rejects the heatcarried by the coolant to the cold heat sink.
 15. A system according toclaim 12, wherein the cold heat sink comprises at least a portion of anaircraft fuselage skin structure.
 16. A system for refrigerating atleast one enclosure comprising: at least one air-to-liquid heatexchanger capable of placing a coolant in a coolant loop in thermalcommunication with at least one interior of the at least one enclosuresuch that the coolant can carry heat away from the at least oneinterior; a liquid-to-direct heat exchanger capable of receiving thecoolant in the coolant loop; and a cold heat sink in thermalcommunication with the liquid-to-direct heat exchanger, wherein the coldheat sink is capable of absorbing the heat carried by the coolantreceived by the liquid-to-direct heat exchanger, and wherein the coldheat sink comprises at least a portion of an aircraft fuselage skinstructure.
 17. A system according to claim 16 further comprising: atleast one pump capable of driving the coolant in the coolant loop.
 18. Asystem according to claim 16, wherein the coolant loop is a closed loopsuch that the at least one air-to-liquid heat exchanger is capable ofreceiving the coolant from the liquid-to-direct heat exchanger after thethe cold heat sink absorbes the heat carried by the coolant.
 19. Asystem for refrigerating at least one enclosure comprising: at least oneair-to-liquid heat exchanger in thermal communication with at least oneinterior of the at least one enclosure; an eutectic thermal battery influid communication with the at least one air-to-liquid heat exchangervia a first coolant loop; a liquid-to-direct heat exchanger in fluidcommunication with the eutectic thermal battery via a second coolantloop, and in thermal communication with a cold heat sink; and at leastone liquid-to-direct heat pump in fluid communication with the eutecticthermal battery via the second coolant loop, and in thermalcommunication with the cold heat sink, wherein the system is capable ofcontrollably operating in at least one of a direct passive mode, anindirect passive mode, a direct active mode and an indirect active modewhereby a coolant is capable of selectively flowing in at least one ofthe first and second coolant loops through at least one of the at leastone air-to-liquid heat exchanger, the eutectic thermal battery, theliquid-to-direct heat exchanger and the at least one liquid-to-directheat pump.
 20. A system according to claim 19, wherein when the systemoperates in the direct passive mode the at least one air-to-liquid heatexchanger is capable of placing the coolant in thermal communicationwith at least one interior such that the coolant can carry heat awayfrom the at least one interior.
 21. A system according to claim 20,wherein when the system operates in the direct passive mode theliquid-to-direct heat exchanger is capable of receiving the coolant suchthat the cold heat sink in thermal communication with theliquid-to-direct heat exchanger can absorb the heat carried by thecoolant.
 22. A system according to claim 21 further comprising aplurality of valves capable of controlling the flow of coolant in thefirst and second coolant loops.
 23. A system according to claim 21,wherein when the system operates in the indirect passive mode the atleast one air-to-liquid heat exchanger is capable of placing the coolantin the first coolant loop in thermal communication with at least oneinterior such that the coolant can carry heat away from the at least oneinterior.
 24. A system according to claim 23, wherein when the systemoperates in the indirect passive mode the eutectic thermal battery iscapable of receiving the coolant from the at least one air-to-liquidheat exchanger and thereafter absorbing the heat carried away by thecoolant.
 25. A system according to claim 24, wherein when the systemoperates in the indirect passive mode the liquid-to-direct heatexchanger is capable of receiving the coolant in the second coolant loopsuch that the cold heat sink in thermal communication with theliquid-to-direct heat exchanger can absorb the heat carried by thecoolant.
 26. A system according to claim 21, wherein when the systemoperates in the direct active mode the at least one air-to-liquid heatexchanger is capable of placing the coolant in the first coolant loop inthermal communication with at least one interior such that the coolantcan carry heat away from the at least one interior.
 27. A systemaccording to claim 26, wherein when the system operates in the directactive mode the at least one liquid-to-direct heat pump is capable ofrejecting the heat carried by the coolant in the first coolant loop tothe cold heat sink.
 28. A system according to claim 26 furthercomprising a store of a pressurized inert composition, wherein theeutectic thermal battery includes an evaporator coil in variable fluidcontact with the store, wherein when the system operates in the directactive mode the eutectic thermal battery is capable of receiving thecoolant from the at least one air-to-liquid heat exchanger andthereafter absorbing the heat carried away by the coolant in the firstcoolant loop, and the pressurized inert composition is capable of beingexpanded into the evaporator coil to thereby carry away the heatabsorbed by the eutectic thermal battery.
 29. A system according toclaim 21, wherein when the system operates in the indirect active modecoolant in the second coolant loop is capable of being placed in thermalcommunication with the eutectic thermal battery such that the coolantcarries heat away from the eutectic thermal battery.
 30. A systemaccording to claim 29, wherein when the system operates in the indirectactive mode the at least one liquid-to-direct heat pump is capable ofrejecting the heat carried by coolant in the second coolant loop.
 31. Asystem according to claim 21 further comprising a store of a pressurizedinert composition, wherein the eutectic thermal battery includes anevaporator coil in variable fluid contact with the store, and whereinthe pressurized inert composition is capable of being expanded into theevaporator coil.
 32. A method of refrigerating at least one enclosurecomprising: refrigerating at least one interior of the at least oneenclosure in a plurality of consecutive modes comprising at least adirect passive mode, an indirect passive mode, a direct active mode andan indirect active mode, wherein the mode of refrigerating is selectedat least partially based upon a temperature of a phase change material,and wherein refrigerating the at least one interior in the indirectpassive mode comprises: placing a coolant in a first coolant loop inthermal communication with the at least one interior such that thecoolant carries heat away from the at least one interior; absorbing theheat carried away by the coolant in the first coolant loop, wherein theheat is absorbed by the phase change material; placing a coolant in asecond coolant loop in thermal communication with the phase changematerial such that the coolant carries away the absorbed heat; andplacing the coolant in the second coolant loop in thermal communicationwith a cold heat sink such that the cold heat sink absorbs the heatcarried by the coolant.
 33. A method according to claim 32, whereinrefrigerating the at least one interior in the direct passive modecomprises: placing a coolant in the first coolant loop in thermalcommunication with the at least one interior such that the coolantcarries heat away from the at least one interior; receiving the coolantinto the second coolant loop and thereafter placing the coolant in thesecond coolant loop in thermal communication with the cold heat sinksuch that the cold heat sink absorbs the heat carried by the coolant,wherein the cold heat sink comprises at least a portion of an aircraftfuselage skin structure.
 34. A method according to claim 32, whereinrefrigerating the at least one interior in the direct active modecomprises: placing the coolant in the first coolant loop in thermalcommunication with the at least one interior such that the coolantcarries heat away from the at least one interior; and rejecting the heatcarried by the coolant in the first coolant loop to the cold heat sink.35. A method according to claim 34, wherein refrigerating the at leastone interior in the indirect active mode comprises: placing the coolantin the second coolant loop in thermal communication with the phasechange material such that the coolant carries away heat from the phasechange material; and rejecting the heat carried by the coolant in thesecond coolant loop to the cold heat sink.
 36. A method according toclaim 34, wherein refrigerating the at least one interior in the directactive mode comprises: placing the coolant in the first coolant loop inthermal communication with the at least one interior such that thecoolant carries heat away from the at least one interior; absorbing theheat carried away by the coolant in the first coolant loop, wherein theheat is absorbed by the phase change material; and expanding apressurized inert composition into thermal communication with the heatabsorbed from the coolant in the first coolant loop such that the inertcomposition carries away the absorbed heat.
 37. A system forrefrigerating at least one enclosure comprising: at least oneair-to-liquid heat pump capable of placing a coolant in a coolant loopin thermal communication with at least one interior of the at least oneenclosure such that the at least one air-to-liquid heat pump can rejectheat from the at least one interior to the coolant to thereby permit thecoolant to carry the heat away from the at least one interior; aliquid-to-direct heat exchanger capable of receiving the coolant in thecoolant loop; and a cold heat sink in thermal communication with theliquid-to-direct heat exchanger, wherein the cold heat sink is capableof absorbing the heat carried by the coolant received by theliquid-to-direct heat exchanger, and wherein the cold heat sinkcomprises at least a portion of an aircraft fuselage skin structure.